Before the advent of dental handpieces driven by air turines at high speeds, the handpieces then used by the dental profession were driven by belts that were energized by an electric motor, the belts extending around pulleys connected to a series of articulated arms, and the dental handpiece was connected to the outer end of the outermost arm and employed a pulley on the outer end of the handpiece which was driven by one of the belts referred to above. Normal speeds for such handpieces range somewhere in the vicinity of 8,000 to 10,000 r.p.m. Modern, high speed handpieces driven by air turbines operate at speeds between 300,000 and 400,000 r.p.m. or higher and dental burs driven at these speeds are far less painful to the patient than the burs driven by the previous slow speed handpieces.
Belt driven handpieces operated at variable speeds by means of controlling the speed of the electric motor through the use of a foot control which primarily comprised a rheostat operated by a pedal extending radially from the foot control and pivoted about a vertical axis. Possibly somewhat resulting from perpetuation of a habit, it has been generally customary to provide control units for such high speed handpieces which employ either a pedal or other means which were movable laterally substantially within a horizontal plane for purposes of varying the speeds of the handpieces. Also, depending upon the posture of a dentist when operating upon a patient, it has been found to be more convenient to operate the foot control by depressing an operating element on the foot control, such as a pedal, annular plate capable of being depressed, or otherwise, whereas in other postures of the dentist, it is more convenient to operate a laterally movable actuating member on the foot control which moves substantially within a horizontal plane.
In view of the foregoing, there is a tendency to provide modern dental foot control units with a plurality of different types of actuating members respectively movably, selectively, in a horizontal plane or a vertical plane. One example of a foot control unit of this type is the subject matter of U.S. Pat. No. 3,471,928, in the name of A. G. Billin, dated Oct. 14, 1969. In this unit, an annular foot-engageable member is adapted to be either depressed or rotated, horizontally, limited distances about the vertical axis of the unit by means of said member being frictionally engaged by the shoe of the dentist. One of the virtues of this control unit is that it can be operated at any location through the full 360.degree. circumference of the annular member.
Not only does the aforementioned patent permit substantially 360.degree. operation of the foot control but, in addition, U.S. Pat. No. 3,596,102, in the name of Gregory W. Brooks, issued July 27, 1971 has an upper, foot-engageable circular member in the form of a relatively flat convex configuration which is intended to be engaged on its upper surface by the foot of a dentist who rotates the member about a central axis of the foot control unit and thereby operates electrical switch mechanism that controls the operation of dental equipment such as handpieces. Only rotary movement of the actuating member is illustrated in said patent and no provision is made for depressing any portion of the perimeter of the circular operating member to actuate the control mechanism.
There also is an earlier U.S. Pat. No. 2,981,915, in the name of R. L. Sonstegard, issued Apr. 25, 1961, which includes a peripheral ring around the lower portion of a circular foot control which is adapted to be pressed radially inward by engagement by the foot of a dentist, for example, for purposes of actuating lever members that operate linkages supporting the movable member of a rheostat to effect variable electrical drive for a dental chair, drill, drill press, or the like. No provision is made for depressing said actuating ring and only inward radial movement is contemplated for actuating the rheostat.
The aforementioned patents illustrate the basic principle of the current types of dental foot control units for dental instruments and especially handpieces are adapted to be operated from substantially any location around the full 360.degree. of the perimeter of the foot control unit. In view of this tendency and trend, the present invention also is adapted to be operated from substantially any major segment of a full 360.degree. perimeter operation of a foot control unit, while also providing certain improvements to render the unit rugged and capable of long life as well as insuring desired convenience and operation by employment of structural features not found in the prior art, without sacrificing any of the advantages of the prior art. Details of such improved structure are set forth below.